Collet assembly and manufacturing process

ABSTRACT

An Improved Collet Assembly and Manufacturing Process is disclosed. Also disclosed is an improved collet that includes a spindle, a center portion comprising several tabs and a collar. The disclosed collet is manufactured from a single piece of stock, and as such, that the tabs are formed from this unitary piece. The disclosed collet is inserted into a collet housing that is further defined by a bore in its center. The preferred collet housing bore is further defined by a sloped portion that cooperates with the tabs formed on the collet to restrain a burr shaft from rotational or axial movement. The collet assembly of the present invention provides improved balance and therefore wear properties over previous collet assembly. In particular, the disclosed collet assembly is well suited for application inside a cannister assembly of a air-powered dental tool handpiece.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to collets or chucks for graspingrotating tool bit shafts and, more specifically, to an Improved ColletAssembly and Manufacturing Process.

2. Description of Related Art

FIG. 1 is a perspective view of a conventional dental handpiece 10within which the device of the present invention might be used. Dentalhandpieces 10 are used to operate "burrs", or rotating cutting tools,similar to conventional drill or router bits, for cutting or grindingteeth or dental appliances. The typical handpiece 10 is designed toreceive compressed air for its operation from a dentist's chair. Thesehandpieces 10 are available in a variety of shapes and sizes, dependingupon their purpose and/or application. As depicted, the handpiece 10comprises a handle 12 and a head 14. A "canister assembly" is housedwithin the head 14. The "canister assembly" comprises, essentially, acompressed air-powered motor with a removable tool shaft 16 heldtherein. The tool shaft 16 in a typical handpiece 10 is removable sothat different burrs or bits may be used so long as they have the samesize tool shaft 16. The tool shaft 16 is held within the canisterassembly by the "collet assembly".

FIG. 1a depicts a typical prior art collet assembly 60. The state of theprior art collet for dental handpieces comprises a tapered portion 62that further has an axial bore 64 drilled into it that is configured toreceive a burr or bit. The burr or bit is held in place by a pair offree-floating wedges 66 that ride in slots 68 formed around thecircumference of the tapered portion 62. Once a burr or bit is insertedinto this prior collet 60, the wedges 66 are biased towards the shaft tohold the shaft in place both axially and rotationally.

There are at two least problems with this prior collet design. First,there are significant manufacturing difficulties in this design. Sincethe typical burr or bit is approximately 0.06 inches in diameter, thewedges and slots must be extremely small--on the order of 0.01 incheswide and 0.1 inches long. Because of the high speed of rotation of theshaft in operation, the shaft must be balanced to high precision. This,in turn necessitates extremely tight tolerances for the wedges andslots. While these tolerances are attainable, it adds considerable costto the manufacturing process. What is needed is a collet that isprecision balanced, but does not require extraordinarily tightmanufacturing tolerances.

The second deficiency with the prior design as shown in FIG. 1a is thelack of self-centering capability. Because the collet is fairlythin-walled, there is a limit to the number of slots that can be cutthrough it before its structural integrity is compromised. The priorcollet, therefore, can only have the two slots and wedges. The problemwith only having two wedges is that the burr or bit is not automaticallycentered by the collet. As stated above, the high rotational speed ofthe collet means that any slight misalignment will result in a shortservice life for the canister and collet (due to wear). What is neededis an improved collet that self-centers the shaft held therein.

SUMMARY OF THE INVENTION

In light of the aforementioned problems associated with the priordevices, it is an object of the present invention to provide an ImprovedCollet Assembly and Manufacturing Process. It is a further object thatthe improved collet of the present invention include a spindle, a centerportion comprising several tabs and a collar. It is an object that thecollet be manufactured from a single piece of stock, and as such, thatthe tabs are formed from this unitary piece. The collet is inserted intoa collet housing that is further defined by a bore in its center. It isan object of this invention that the collet housing bore is furtherdefined by a sloped portion that cooperates with the tabs formed on thecollet to restrain a burr shaft from rotational or axial movement. It isa still further object that the collet assembly of the present inventionprovide improved balance and therefore wear properties over previouscollet assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention, which are believed tobe novel, are set forth with particularity in the appended claims. Thepresent invention, both as to its organization and manner of operation,together with further objects and advantages, may best be understood byreference to the following description, taken in connection with theaccompanying drawings, of which:

FIG. 1 is a perspective view of a dental handpiece;

FIG. 1a is a perspective view of a typical prior collet assembly;

FIG. 2 is a side view of the head of a dental handpiece;

FIG. 3 is a cutaway side view of a preferred canister assembly of thepresent invention;

FIG. 4 is a partial cutaway side view of a preferred collet assembly ofthe present invention;

FIG. 5 is a pair of partial cutaway side views of the collet assembly ofFIG. 4, depicting the restraining action of the preferred tab;

FIG. 6 is a side view of a preferred collet; and

FIG. 7 is a partial cutaway side view of the collet of FIG. 6, depictingthe preferred cross-section of the collet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled inthe art to make and use the invention and sets forth the best modescontemplated by the inventor of carrying out his invention. Variousmodifications, however, will remain readily apparent to those skilled inthe art, since the generic principles of the present invention have beendefined herein specifically to provide an Improved Collet Assembly andManufacturing Process.

The present invention can best be understood by initial consideration ofFIG. 2. FIG. 2 is a side view of the head 18 of a dental handpiece (seeFIG. 1). The head 18 houses, among other things, the collet assembly 20.The collet assembly 20 is configured to accept a tool shaft 16 andrestrain it from rotational or axial motion with respect to the colletassembly 20. In order to remove the tool shaft 16, one need simply presson the release button 22 and pull axially (away from the collet assembly20) on the tool shaft 16.

Now turning to FIG. 3, one may better understand the unique attributesof the present invention. FIG. 3 is a cutaway side view of a preferredcanister assembly 24 of the present invention. The canister assembly 24typically is inserted into the head after first unscrewing the releasebutton (see FIG. 2). The canister assembly 24 comprises a canisterhousing 26 within which the collet assembly 28 rotates. The colletassembly 28 rotates on a pair of bearing assemblies 30 that aretypically pressed onto the collet assembly 28 and then are each sealedto the canister housing 26 by an O-ring 32. These bearing assemblies 30and O-rings 32 are in use in conventional canister assemblies. Thecollet assembly 28 is caused to rotate when compressed air is directedacross the turbine 34. The turbine 34 is simply a single-stage fan inits function. As describe above, the tool shaft 16 is held in the colletassembly 28, and therefore will rotate with the collet assembly 28.

The unique collet assembly 28 of the present invention comprises acollet housing 36, though which is an axial housing bore 70, withinwhich is a collet 38, a spring 40 and a retainer 42. The collet 38 isfurther defined by a collar 44 at its front end, and a spindle 46 at itsrear end. The tool shaft 16 slides into the collet 38 through the collar44, and is held in the collet 38 by the interference fit between theshaft 16 and the collet 38; further detail regarding this situation isfound below in connection with FIGS. 4-7. The collet 38 is urged againstthe collet housing 36 as a result of the spring 40 pressing against thecollar 44. If sufficient axial force is applied to the spindle 46 tooppose the spring 40, the collet 38 will no longer be in contact withthe collet housing 36. This axial force is provided by a user pressingon the release button (see FIG. 2), which in turn will contact thespindle. The spring 40 and collet 38 are retained within the collethousing 36 by the retainer 42. The retainer 42 is attached to the collethousing 36, preferably via an interference fit. The materials ofconstruction of all of these elements (with the exception of theO-rings) is metal, as is well known in the art.

FIG. 4 provides illumination regarding the unique collet design and theprocess for making it. FIG. 4 is a partial cutaway side view of apreferred collet assembly of the present invention. As can be seen, thecollet 38 comprises a spindle 46 and a collar 44, which are connected toone another by a plurality of struts 48 (only one shown here). Thecollet 38 also comprises a plurality of tabs 50 (only one is shown),that are separated from the spindle 46 by a aperture 52. The collar 44,tabs 50, struts 48 and spindle 46 form a bore 54 in the center of thecollet 38. It should be noticed that the collet housing 36 is defined bya tapered portion 56 on its interior surface that is configured tointeract with the tabs 50. It should further be noticed that the tabs 50are thicker than the struts 48, and as such, will contact the taperedportion 56 before the struts 48, as the collet 38 is moved in direction"A".

Once the tool shaft 16 is inserted into the bore 54, the collet 38 isbiased rearwardly in the direction of arrow "A" (see spring discussionabove) until the tabs 50 are pressed against the tool shaft 16 by thetapered portion 56 of the housing. If the collet 38 is moved in thedirection opposite arrow "A", the interference forces between thetapered portion 56, the tabs 50, and the tool shaft 16 will be removed,and the tool shaft 16 will slip easily out of the bore 54.

A discussion of the unique process to manufacture this unique collet isnow in order. First, a piece of solid metal stock is machined to havethe outer surface shape and dimensions of the collet 38 depicted inFIGS. 3 and 4. A hole, having a diameter smaller than that of the toolshaft 16 is drilled through the center of the piece from the collar 44to the spindle 46. The apertures 52 and slots (see FIGS. 6 and 7) arethen cut to free the tabs 50 from the struts 48. Next, the hole isreamed out to the final diameter that will permit the tool shaft 16 tobe inserted. Since the tabs 50 were free-floating when the hole wasreamed out, they will not be reamed (or made thinner) during this boringstep, but will simply deflect out of the way of the cutting tool. Theresult is a simple, tight tolerance, low-cost method for creating thesetabs 50 that are thicker than the struts 48, in a collet 38 formed in aunitary piece.

FIG. 5 gives another depiction of the operation of the presentinvention. FIG. 5 is a pair of partial cutaway side views of the colletassembly of FIG. 4, depicting the restraining action of the preferredtabs 50. View A depicts the tool shaft 16 in a restrained conditioninside of the collet 38. As is depicted, the tab 50 is being forcedagainst the tool shaft 16 by the tapered portion 56 of the collethousing 36. View B depicts the tool shaft 16 in an un-restrainedcondition inside of the collet 38. As can be seen, the collet 38 hasmoved to the left in the diagram, and the tab 50 has become disengagedfrom the collet housing 36, thereby releasing the tool shaft 16 to beremoved.

Now turning to FIG. 6, we can gain an even better understanding of theimproved collet 38 of the present invention. FIG. 6 is a side view of apreferred collet 38. The collet 38 is preferably cylindrical in shape,and is defined by a plurality of tabs 50 and struts 48. Between each tab50 and strut 48 is a slot 58 that connects to the bore (not shown) andseparates each strut 48 from the adjacent tabs 50. Each tab 50 isfurther separated at one end from the spindle 46 by an aperture 52, andas such, the tabs 50 are free to deflect outwardly and inwardly, asnecessary.

FIG. 7 is presented to provide further detail regarding the collet 38.FIG. 7 is a partial cutaway side view of the collet 38 of FIG. 6,depicting the preferred cross-section of the collet along the line A--A.In the depicted embodiment, there are three struts 48, separated fromthe three tabs 50 by six slots 58 that penetrate from the outer surfaceof the collet 38 to the inner bore 54. In the depicted form, there willbe an even and balanced (three-sided) force against the tool shaft (seeprevious figures) by the tabs 50. This balanced force will also causethe tool shaft to be self-centered, without the need for the specialmanufacturing tolerances of the prior devices. These designcharacteristics result in well-balanced rotation.

In its preferred form, the present canister assembly 24 will sustain acollet assembly 28 rotational velocity of 510 to 530 revolutions perminute, as compared to 460 RPM for a conventional unit. Furthermore, thebalanced design and easy repeatability has resulted in twice thelongevity of the conventional canister assembly 24.

One should understand that while the present embodiment depicts a"rear-release" collet, the present unique collet design is easilyreconfigured to permit pressure on the front of the collet to releasethe shaft. The rear-release collet is a necessity for the dentalhandpiece application to prevent blood and other foreign matter fromentering the open end of the collet and thereby causing the tool shaftto be jammed therein.

It should furthermore be appreciated that the present invention isreadily adaptable to hold any diameter of burr or bit, if desired. Inother words, a larger version of the same collet assembly would functionidentically to that previously-described, and with the same advantages.The difference is simply one of scale.

Those skilled in the art will appreciate that various adaptations andmodifications of the just-described preferred embodiment can beconfigured without departing from the scope and spirit of the invention.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention may be practiced other than as specificallydescribed herein.

What is claimed is:
 1. An improved collet assembly for holding a toolshaft, comprising:a collet defined by an axial collet bore adapted toreceive said shaft, and a plurality of tabs integral to said collet andadjacent to said bore; a collet housing including an axial housing boreadapted to receive said collet and further including a tapered portion,whereby said tabs cooperate with said tapered portion to hold said toolshaft; and further comprising biasing means for biasing said tabstowards said tapered portion, said biasing means comprising a spring. 2.The collet assembly of claim 1, wherein:said collet comprises:a spindle;a center portion extending from said spindle and comprising said tabs;and a collar adjacent to said center portion; and wherein said axialcollet bore penetrates said collar and said center portion.
 3. Thecollet assembly of claim 2, wherein said center portion furthercomprises a plurality of struts extending between said spindle and saidcollar.
 4. The collet assembly of claim 1, wherein said biasing meansexerts biasing force at said collar.
 5. The collet assembly of claim 4,wherein:said collet housing further comprises a first end and a secondend, with said axial housing bore extending from said first end to saidsecond end; said collet assembly further comprises a retainer attachedin said housing bore between said first end and said biasing means; andsaid spindle extends out of said second end.
 6. The collet assembly ofclaim 5, wherein said collet comprises a unitary piece.